Magnetron with rotatable tuning means

ABSTRACT

A co-axial magnetron is constructed to permit rapid cyclic variation of its output frequency. An annular cavity defined by an annular wall surrounding a central anode is dimensioned to provide an electric field which varies for different angular directions and is provided with a dielectric body which can be rotated rapidly through the varying electric field with corresponding variations in output frequency.

United States Patent Esteron et al.

[ Aug. 12, 1975 MAGNETRON WITH ROTATABLE TUNING MEANS Inventors: Maurice Esteron; Robert Bernard Coulson, both of Chelmsford, England Assignee: English Electric Valve Company Limited, Chelmsford, England Filed: Sept. 20, 1974 Appl. No.: 507,594

Related US. Application Data Continuation of Ser. No. 371,684, June 20, 1973, abandoned.

Foreign Application Priority Data June 22, 1972 United Kingdom 29227/72 US. Cl. 3l5/39.6l; 315/3755; 315/37.77 Int. Cl. HOlJ 25/50 Field of Search 315/3951, 39.61, 39.77,

[56] References Cited UNITED STATES PATENTS 3,412,285 11/1968 Gerard 315/3977 X 3,435,284 3/1969 Downing et al.... 315/3977 X 3,441,796 4/1969 Cooper 315/3961 3,590,312 6/1971 Blank et a1 315/3977 3,731,137 5/1973 Foreman 315/3977 Primary ExaminerSaxfield Chatmon, Jr. Attorney, Agent, or F irmBa1dwin, Wight & Brown [5 7] ABSTRACT A co-axial magnetron is constructed to permit rapid cyclic variation of its output frequency. An annular cavity defined by an annular wall surrounding a central anode is dimensioned to provide an electric field which varies for different angular directions and is provided with a dielectric body which can be rotated rapidly through the varying electric field with corresponding variations in output frequency.

18 Claims, 6 Drawing Figures PATENTED AUG 1 2191s MAGNETRON WITH ROTATABLE TUNING MEANS This is a continuation of Ser. No. 37 l ,684 filed June 20. 1973, now abandoned.

This invention relates to magnetrons and more specifically to co-axial magnetrons. The object of the invention is to provide improved and relatively simple coaxial magnetrons'the tuning of which can be varied cyclically and rapidly over a required range. This requirement arises in a number of cases, notably in magnetrons for so-called Frequency Agility Radars. This requirement is difficult to satisfy in an economic and mechanically reliable manner especially when high frequency tuning rates are required. The present invention seeks to overcome this difficulty.

The invention is illustrated in and explained in connection with the accompanying drawings in which FIGS. 1 and 2, which are provided for purposes of preliminary explanation, are schematic mutually perpendicular views of a known co-axial magnetron (no means of varying the centre frequency or providing rapid frequency variation are shown in these figures) showing magnetic field, electric field and current directions in the magnetron;

FIGS. 3 and 4 are schematic mutually perpendicular views of one embodiment of the invention; and

FIGS. 5 and 6 are schematic mutually perpendicular views of another embodiment of the invention.

Like references denote like parts in all the figures.

In a co-axial magnetron, as is well known, alternate cavities in the interaction space of the magnetron are coupled to the main cavity (which, in the usual con struction, surrounds the interaction space) in such manner as to cause said main cavity to be excited as a co-axial resonator. One of the more important practical advantages of the co-axial magnetron is that the internal space of the main cavity (i.e. in a co-axial magnetron with the main cavity outside the interaction space, the space between the outer cylindrical wall of said cavity and the internal anode cylinder enclosing the interaction space) can be and sometimes is outside the evacuated envelope. For example, in one known and good construction of this nature the internal anode is enclosed in a ceramic cylinder which forms part of the vacuum envelope of the magnetron, so that all tuning arrangements for the main cavity and means for coupling the main cavity to an external load are outside the vacuum.

FIGS. 1 and 2 schematically represent a typical known co-axial magnetron. Because the purpose of these figures is merely to show the magnetic field, electric field and current flow directions, no tuning or loadcoupling means are shown. Referring to these figures 1 represents an axial cathode, 2 is an internal anode surrounding the interaction space, 3 are radial vanes projecting inwards towards the cathode from said anode 2 and 4 is the outer wall of the main surrounding coaxially resonating cavity. The direction of the electric field is represented by the arrow headed dotted line E in FIG. 1; that of the magnetic field by the arrow headed chain lines B in FIG. 2; and those of the currents in the anode 2 and in the outer wall 4 of the main cavity by the arrow headed broken lines I. The electric field is of maximum intensity about midway between the anode 2 and the outer wall 4. As will be seen neither the electric field or the current flow lines have any axial component.

Broadly speaking there are two known ways of varying the centre frequency or providing rapid frequency variation of a magnetron as represented in FIGS. 1 and 2 in order to cause the generated frequency to be changed cyclically, for example in order to make the magnetron suitable for a Frequency Agility Radar. One method is to move an end wall of the main cavity back and forth in a direction parallel to the axis of the magnetron to vary the cavity tuning. For example the said end wall may be of diaphragm construction and be moved back and forth in the required manner by a suitable driving arrangement. This can be done without sensibly disturbing the electric field or current flow lines because substantially no current flows radially across the junctions between said end wall and the inner and outer cylinders 2 and 4. This method of varying the tuning is, however, unsatisfactory mechanically if the required frequency of variation is to be over 200 times per second. Clearly, reciprocating the said end wall at a frequency of this order of magnitude involves very high accelerations resulting in stresses in the moving parts, or the parts to which they are attached, which are so high as to be impractical, or nearly so.

In the second method of tuning variation, the magnetron is provided with a plurality of vanes of dielectric material which are inside the main cavity, each being so mounted that it can be rotated about an axia parallel to the axis of the magnetron. In the usual arrangement of this nature the axes of the dielectric vanes are parallel to the magnetron axis equally spaced along an imaginary circle mid-way between the outer cavity wall 4 and the internal anode 2. Suitable driving means are provided for rotating the dielectric vanes together on their axes, so that said vanes pass through positions in which they lie along the lines of the electric field in the main cavity and positions in which they lie at right angles thereto. In the former positions the vanes reduce the frequency of the cavity to a substantial extent (as compared to a similar cavity without dielectric vanes); in the latter positions the frequency is reduced to a much smaller extent. Thus, upon rotation of the vanes, the cavity frequency is varied cyclically, maximum frequency variation being obtained if all the vanes are rotated synchronously.

This second method of tuning variation has the defect of being mechanically complex and expensive for obviously it is difficult mechanically to rotate a considerable number of vanes for example six or eight of them in synchronism. Moreover, owing to windage losses, the power required to rotate the vanes at the required high speed may be considerable, especially if, as is often the case with high power magnetrons, it is necessary to pressurise the interior of the main cavity.

According to this invention the co-axially resonant main cavity of a co-axial magnetron is so formed or constructed as to have, in its interior space, spaced regions of substantially different electric field intensity and cyclic variation of tuning is effected by a rotary member carrying at least one dielectric member which, upon rotation of said rotary member, is caused to move successively through said spaced regions.

Preferably the rotary member is of symmetrical construction carrying an even number of dielectric members.

The rotary member may be of dielectric construction with the dielectric member or members constituted by portions made of material of substantially higher dielectric constant than the remainder of the rotary member.

The spaced regions of different electric field intensity may be produced by reducing over one or more angles of arc, the radial cross section of the cavity presented to the electric field lines. This may conveniently be done by providing one or more conductive projections, extending each over a pre-determined angle of are, on one of the circular walls of the cavity (preferably on the outer wall) and extending towards the other circular wall and the dielectric members may be constituted by one or more arcuate dielectric members so mounted on the rotary member that, on rotation thereof, each passes endwise through the space between the stepped cavity wall and the other wall of the main cavity. In such a construction a satisfactory form for the rotary member is that of a cylinder with equally spaced arcuate portions of material of substantially higher dielectric constant than the remainder of the cylinder.

In another embodiment the aforesaid spaced regions of different electric field intensity are produced by reducing, over one or more angles of arc, the radial cross section of the main cavity presented to the electric field lines, the required reduction or reductions of cross section being obtained by providing one or more arcuate projections on one of the circular walls (again preferably the outer wall) of the main cavity, each of said projection being slotted with a slot in a plane perpendicular to the magnetron axis, and there being at least one dielectric member in the ,form of a sector or truncated sector shaped dielectric body carried by the rotary member and so mounted thereon that, on rotation thereof, it passes through the slot or slots. In such a construction a satisfactory form for the rotary member is that of a flange or disc with equally spaced sector or truncated sector shaped portions of material of substantially higher dielectric constant than the remainder of the flange or disc.

FIGS. 3 and 4 show, in manner similar to FIGS. 1 and 2, one embodiment of the invention. In FIGS. 3 and 4 the outer wall 4 of the main cavity is provided with a pair of similar, oppositely disposed, inward projections 41 (shown crossed hatched in FIG. 4) so that the inner surface of the effective wall 4 is inwardly stepped where these occur, thus reducing the radial cross section presented to the electric field lines and therefore substantially increasing the electric field intensity at these regions. The rotary member is a cylinder 5 of dielectric material mounted on or forming part of an end disc 51. The dielectric members, (also shown cross hatched in FIG. 4) are constituted by oppositely disposed portions 52 of the cylinder and arc made of material of substantially higher dielectric constant than that of the rest of the cylinder. If desired the dielectric members 52 may be separate members i.e. the other parts of the cylinder 5 may be omitted. If this construction is adopted the leading and trailing edges of the members 52 are preferably pointed or otherwise contoured to reduce air resistance to motion. When the members 52 are in the positions shown in FIG. 4 they are in regions of least electric field intensity and therefore reduce the frequency of the cavity to the least ex tent. When they are at right angles to the positions shown in FIG. 4, i.e. when the rotary member has been rotated through 90 from the position shown in FIG. 4, the members 52 will be in regions of maximum electric field intensity and therefore they will reduce the cavity frequency to the maximum extent.

In FIGS. 3 and 4 only two inward projections 41 and only two dielectric members are shown. The number of projections and/or of dielectric members however, can be increased with consequent increase in the number of cyclic variations of tuning in one revolution of the carrier member, although increase in the number of projections will be accompanied by decrease in the range frequency variation because of the accompanying reduction of increase in electric field intensity caused by each of them.

In the modification shown in FIGS. 4 and 5 the outer wall of the main cavity is again provided with inward projections 41 but these are radially slotted with slots 42. As shown the rotary member is in the form of a flange 6 having truncated sector shaped, oppositely disposed portions 61 which are of substantially higher dielectric constant than the rest of the flange and constitute the dielectric members, said flange being mounted on or formed with a supporting cylinder 62 on an end disc 63. However, the parts of the flange between the dielectric members 61 may be omitted. When the dielectirc members 61 are in the slots 42 they have least effect on the resonant frequency of the main cavity (being then in the slots) but, when the rotary member has rotated through from that shown in FIG. 6, they are in regions of electric field and have maximum effect on the resonant frequency. As in the case of the embodiment of FIGS. 3 and 4 more than two projections and/or dielectric members may be provided. For high speed working any convenient means, for example strengthening rings, may be provided, if necessary, to prevent outer movement of the dielectric members under centrifugal force if said members are separate from one another.

We claim:

1. A tunable coaxial magnetron comprising in combination:

a cathode member;

an anode member defining a plurality of radially disposed cavity resonators disposed adjacent to said cathode member and presenting an outer cylindrical wall surface;

an outer wall member surrounding said anode member and presenting an inner cylindrical wall surface defining with said outer cylindrical wall surface an annular resonant main cavity disposed coaxially with respect to said anode member and along the annular path of which an electric field is generated; means for producing at least one region of locally intensified electric field along the annular path of said main cavity, said means comprising at least one conductive projection on one of said wall surfaces, such projection extending radially toward the other wall surface whereby locally to reduce the radial cross section presented to the electric field; and

a rotary tuning member including at least one dielectric member within said main cavity and means for rotating said tuning member to cause the dielectric member to move periodically through said region of locally intensified electric field to effect cyclic variation of tuning.

2. A co-axial magnetron according to claim 1 wherein the rotary member is of symmetrical construction carrying an even number of dielectric members.

3. A co-axial magnetron according to claim 1 wherein the rotary member is of dielectric construction with the dielectric member constituted by portions made of material of substantially higher dielectric constant than the remainder of the rotary member.

4. A co-axial magnetron according to claim 1 wherein said means comprises a plurality of spaced conductive projections, each extending over a predetermined angle of arc, on one of the walls of the cavity and extending towards the other wall to define spaced regions of locally intensified electrical field and the dielectric member is constituted by an arcuate dielectric member so mounted on the rotary member that, on rotation thereof, it passes endwise through said spaced regions.

5. A co-axial magnetron according to claim 4 wherein the rotary member is in the form of a cylinder with an arcuate portion of material of substantially higher dielectric constant than the remainder of the cylinder.

6. A co-axial magnetron according to claim 1 wherein said projection is arcuate and extends over an angle of arc on one of the walls of the main cavity, said projection being slotted with a slot in a plane perpendicular to the magnetron axis, and there being at least one dielectric member in the form of a truncated sector shaped dielectric body carried by the rotary member and so mounted thereon that, on rotation thereof, it passes through the slot.

7. A co-axial magnetron according to claim 6 wherein the form of the rotary member is that of a disc with equally spaced truncated sector shaped portions of material of substantially higher dielectric constant than the remainder of the disc.

8. A tunable coaxial magnetron comprising, in combination:

anode-cathode means defining an interaction region;

wall means defining an annular resonating cavity coaxial with and surrounding said interaction region and electromagnetically coupled therewith to provide an electric field of closed path annular form within said cavity;

means extending from said wall means for locally constricting the radial width of said cavity to cause said electric field to be of locally different field intensities along the closed path thereof; and

means for rapidly dithering the frequency of said cavity and comprising a member within said cavity mounted for rotation coaxially thereof and having at least one dielectric member movable along said path, said dielectric member being of a length to occupy only a portion of said path whereby successively to move through said regions of different field intensity to effect cyclic variation of tuning.

9. A coaxial magnetron as recited in claim 1 wherein said means last mentioned is of symmetrical construction carrying an even number of dielectric members.

10. A coaxial magnetron as recited in claim 1 wherein said means last mentioned is of dielectric construction with the dielectric member constituted by portions made of material of substantially higher dielectric constant than the remainder of the rotary member.

11. A coaxial magnetron as recited in claim 1 wherein the means for locally constricting the radial width of said cavity is a conductive projection, extending over a predetermined angle of arc, on said wall means and wherein said dielectric member is constituted by an arcuate dielectric member so mounted on said means for rapidly dithering the frequency of said cavity that, on rotation thereof, it passes endwise through the local constriction presented by said projec tion.

12. A coaxial magnetron as recited in claim 1 wherein said means last mentioned is in the form of a cylinder with an arcuate portion of material of substantially higher dielectric constant than the remainder of the cylinder.

13. A coaxial magnetron as recited in claim 1 wherein the form of said means last mentioned is that of a disc with equally spaced truncated sector shaped portions of material of substantially higher dielectric constant than the remainder of the disc.

14. A tunable coaxial magnetron comprising in combination:

a cathode member;

an anode member defining a plurality of radially disposed cavity resonators disposed adjacent to said cathode member and including an outer cylindrical wall surface; an outer wall member surrounding said anode member and including an inner cylindrical wall surface defining with said outer cylincrical wall surface an annular resonant main cavity disposed coaxially with respect to said anode member and along the annular path of which an electric field is generated;

means for producing along the annular path of said main cavity spaced regions of locally intensified electric field, said means comprising a plurality of conductive projections on one of said cylindrical wall surfaces, each extending over a predetermined angle of arc and projecting radially toward the other of said cylindrical wall surfaces whereby locally to reduce the radial cross section presented to the electric field; and

a rotary tuning member including at least one dielectric member extending along a portion only of said path and means for rotating said tuning member to cause the dielectric member to move successively through said spaced regions to effect cyclic variation of tuning.

15. A coaxial magnetron as recited in claim 14 wherein the rotary tuning member is of symmetrical construction carrying an even number of dielectric members.

16. A coaxial magnetron as recited in claim 14 wherein the rotary tuning member is of dielectric construction with the dielectric member constituted by portions made of material of substantially higher dielectric constant than the remainder of the rotary member.

17. A coaxial magnetron as recited in claim 14 wherein the rotary tuning member is in the form of a cylinder with an arcuate portion of material of substantially higher dielectric constant than the remainder of the cylinder.

18. A coaxial magnetron as recited in claim 14 wherein the form of the rotary tuning member is that of a disc with equally spaced truncated sector shaped portions of material of substantially higher dielectric constant than the remainder of the disc.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3,899,715

DATED I August 12, 1975 INVENTOWS) 1 Maurice Esterson and Robert Bernard Coulson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the patent heading, change Esteron et al." to --Esterson et al.; and

after "Inventors:" change "Maurice Esteron" to Maurice Esterson-.

Signed and Emailed this A ttes t:

RUTH C. MASON Arresting Officer C. MARSHALL DANN Commissioner ufParents and Trademarks 

1. A tunable coaxial magnetron comprising in combination: a cathode member; an anode member defining a plurality of radially disposed cavity resonators disposed adjacent to said cathode member and presenting an outer cylindrical wall surface; an outer wall member surrounding said anode member and presenting an inner cylindrical wall surface defining with said outer cylindrical wall surface an annular resonant main cavity disposed coaxially with respect to said anode member and along the annular path of which an electric field is generated; means for producing at least one region of locally intensified electric field along the annular path of said main cavity, said means comprising at least one conductive projection on one of said wall surfaces, such projection extending radially toward the other wall surface whereby locally to reduce the radial cross section presented to the electric field; and a rotary tuning member including at least one dielectric member within said main cavity and means for rotating said tuning member to cause the dielectric member to move periodically through said region of locally intensified electric field to effect cyclic variation of tuning.
 2. A co-axial magnetron according to claim 1 wherein the rotary member is of symmetrical construction carrying an even number of dielectric members.
 3. A co-axial magnetron according to claim 1 wherein the rotary member is of dielectric construction with the dielectric member constituted by portions made of material of substantially higher dielectric constant than the remainder of the rotary member.
 4. A co-axial magnetron according to claim 1 wherein said means comprises a plurality of spaced conductive projections, each extending over a predetermined angle of arc, on one of the walls of the cavity and extending towards the other wall to define spaced regions of locally intensified electrical field and the dielectric member is constituted by an arcuate dielectric member so mounted on the rotary member that, on rotation thereof, it passes endwise through said spaced regions.
 5. A co-axial magnetron according to claim 4 wherein the rotary member is in the form of a cylinder with an arcuate portion of material of substantially higher dielectric constant than the remainder of the cylinder.
 6. A co-axial magnetron according to claim 1 wherein said projection is arcuate and extends over an angle of arc on one of the walls of the main cavity, said projection being slotted with a slot in a plane perpendicular to the magneTron axis, and there being at least one dielectric member in the form of a truncated sector shaped dielectric body carried by the rotary member and so mounted thereon that, on rotation thereof, it passes through the slot.
 7. A co-axial magnetron according to claim 6 wherein the form of the rotary member is that of a disc with equally spaced truncated sector shaped portions of material of substantially higher dielectric constant than the remainder of the disc.
 8. A tunable coaxial magnetron comprising, in combination: anode-cathode means defining an interaction region; wall means defining an annular resonating cavity coaxial with and surrounding said interaction region and electromagnetically coupled therewith to provide an electric field of closed path annular form within said cavity; means extending from said wall means for locally constricting the radial width of said cavity to cause said electric field to be of locally different field intensities along the closed path thereof; and means for rapidly dithering the frequency of said cavity and comprising a member within said cavity mounted for rotation coaxially thereof and having at least one dielectric member movable along said path, said dielectric member being of a length to occupy only a portion of said path whereby successively to move through said regions of different field intensity to effect cyclic variation of tuning.
 9. A coaxial magnetron as recited in claim 1 wherein said means last mentioned is of symmetrical construction carrying an even number of dielectric members.
 10. A coaxial magnetron as recited in claim 1 wherein said means last mentioned is of dielectric construction with the dielectric member constituted by portions made of material of substantially higher dielectric constant than the remainder of the rotary member.
 11. A coaxial magnetron as recited in claim 1 wherein the means for locally constricting the radial width of said cavity is a conductive projection, extending over a predetermined angle of arc, on said wall means and wherein said dielectric member is constituted by an arcuate dielectric member so mounted on said means for rapidly dithering the frequency of said cavity that, on rotation thereof, it passes endwise through the local constriction presented by said projection.
 12. A coaxial magnetron as recited in claim 1 wherein said means last mentioned is in the form of a cylinder with an arcuate portion of material of substantially higher dielectric constant than the remainder of the cylinder.
 13. A coaxial magnetron as recited in claim 1 wherein the form of said means last mentioned is that of a disc with equally spaced truncated sector shaped portions of material of substantially higher dielectric constant than the remainder of the disc.
 14. A tunable coaxial magnetron comprising in combination: a cathode member; an anode member defining a plurality of radially disposed cavity resonators disposed adjacent to said cathode member and including an outer cylindrical wall surface; an outer wall member surrounding said anode member and including an inner cylindrical wall surface defining with said outer cylincrical wall surface an annular resonant main cavity disposed coaxially with respect to said anode member and along the annular path of which an electric field is generated; means for producing along the annular path of said main cavity spaced regions of locally intensified electric field, said means comprising a plurality of conductive projections on one of said cylindrical wall surfaces, each extending over a predetermined angle of arc and projecting radially toward the other of said cylindrical wall surfaces whereby locally to reduce the radial cross section presented to the electric field; and a rotary tuning member including at least one dielectric member extending along a portion only of said path and means for rotating said tuning member to cause the dielectric member to move successively through said spaced regions To effect cyclic variation of tuning.
 15. A coaxial magnetron as recited in claim 14 wherein the rotary tuning member is of symmetrical construction carrying an even number of dielectric members.
 16. A coaxial magnetron as recited in claim 14 wherein the rotary tuning member is of dielectric construction with the dielectric member constituted by portions made of material of substantially higher dielectric constant than the remainder of the rotary member.
 17. A coaxial magnetron as recited in claim 14 wherein the rotary tuning member is in the form of a cylinder with an arcuate portion of material of substantially higher dielectric constant than the remainder of the cylinder.
 18. A coaxial magnetron as recited in claim 14 wherein the form of the rotary tuning member is that of a disc with equally spaced truncated sector shaped portions of material of substantially higher dielectric constant than the remainder of the disc. 